Abstract
The specific length of a tunnel (STL) and a new analytical model for calculating the block surface area of the rock mass are introduced. First, a method for determining the appropriate length of a tunnel for a numerical simulation is described. The length is then used to examine the correlation between the inflow rate to the tunnel and the block volume, the block surface area, and the fracture intensity (P32) through analytical and numerical modeling. The results indicate that the length of the tunnel should at least be equal to the least common multiple (LCM) of the apparent spacings of the joint sets at the wall of the tunnel to obtain the more reliable and immediate results for the inflow rate to a tunnel that is excavated in a fractured rock mass. A new analytical model was developed to calculate the block surface area and determine the essential joint set parameters, which include the dip, dip direction, and spacing. The determination of the rock block characteristics through numerical modeling requires considering the intact block for calculations. The results indicated that the inflow rate to the tunnel increased with an increase in fracture intensity and a decrease in block volume and surface area. The STL and the analytical model used for calculating the block surface area are validated through numerical simulations with 3DEC software version 7.0.
Highlights
Quality information on the inflow rate to an underground excavation is useful in a wide range of civil works
The last section of this paper focuses on the evaluation of the relationship between the tunnel inflow rate and three other parameters, which include block volume, block surface area, and volumetric fracture intensity
Using the concept of specific length of a tunnel (STL), which is explained and validated in Section 2, a2,series of of numerical simulations are designed to study the relationship between geometrical numerical simulations are designed to study the relationship between geometrical charcharacteristics of rock the rock block, rock block volume, block surfacearea, area,and andvolumetric volumetric acteristics of the block, i.e.,i.e., rock block volume, block surface fractureintensity intensityononthe the one hand and inflow to tunnel the tunnel onother the other fracture one hand and thethe inflow raterate to the on the hand.hand
Summary
Quality information on the inflow rate to an underground excavation is useful in a wide range of civil works. The inflow rate is effectively a determining parameter for the cost of a civil and mining engineering project. Previous studies that aimed to estimate the inflow rate to a tunnel were developed through empirical, analytical, and numerical methods. Many of the empirical equations that have been developed for estimating the inflow rate to a tunnel consider increasing depth, which results in the permeability of the rock mass decreasing and the hydraulic gradient at the wall of the tunnel increasing [7,8,9]. The developed empirical equations are based on data obtained from the double packer [10] or Lugeon tests [11] for the hydraulic conductivity of the rock mass. Several investigations have been conducted for adjusting the relationships between the permeability of the rock mass and its geological indices [12,13], e.g., RQD, RMR, and GSI
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